bevy_text::input module with no undo

[Zeophlite]

Objective

• bevy_text::input module #20336 without undo/redo (see Temporarily upstream undo_2 #20489 to upstream the undo_2 library)

Testing

• CI

[mockersf]

I've played a bit with this PR and how to use it, and I think it introduces too many things at once, and some that doesn't interact well together.

I would prefer a simpler PR that would introduce a component that holds a cosmic buffer, and how to interact with it. Making it smaller would also improve the code organisation.

I don't think this should be merged in this state.

[Zeophlite]

and some that doesn't interact well together

@mockersf Could you expand on this point?

[Zeophlite]

I've taken the time to split up input.rs

[Zeophlite]

I have also taken the time to adopt #20326 , rebase onto this branch - see #20826

This was very helpful in fleshing out some concepts, such as "submit"

I appreciate any feedback on either repo on what parts should be pulled out to help merge these

[Zeophlite]

This version has removed clipboard, filtering, masking, they will be re-added as separate PRs

[rdrpenguin04]

One element I would personally consider critical for an example is handling text input on a mobile browser, i.e. by popping open an on-screen keyboard when a text input is focused. This definitely feels like it belongs more in the eventual widget code, but it also would feel right to have that kind of support within Bevy (experimentally?) so work wouldn't need to be duplicated across many projects.